It is known that, in a telecommunication network, traffic exchanged by users may be transported either by a circuit-switch mechanism or a packet-switch mechanism.
In a circuit-switched network, a circuit connecting two users wishing to exchange traffic is allocated within the network. Such a circuit is then used exclusively for transporting traffic exchanged by such two users in the form of synchronous or plesiochronous TDM (Time Division Multiplexing) traffic flows. When the two users stop exchanging traffic, the circuit is de-allocated. Exemplary circuit-switched networks are the PDH networks and the SDH or SONET networks.
In a packet-switched network, traffic generated by each user is split into packets. Each packet is then tagged with a destination address and is independently routed span-by-span according to its destination address, until it reaches the destination user. At the destination user, packets are sorted and the original content of the traffic is recovered. Exemplary packet-switched networks are the Ethernet networks and the MPLS (Multi-Protocol Label Switching) networks.
Recently, the so-called “circuit emulation services” are becoming more and more widespread. Such circuit emulation services allow to transport TDM traffic flows (e.g. synchronous SDH flows) exchanged by two users (e.g. two SDH networks) by means of a packet-switched network (e.g. an Ethernet network) “emulating” the allocation of a circuit. In other words, the two users exchange traffic in form of TDM traffic flows without realizing that, actually, such TDM traffic flows are not transported by a circuit, but they are transported in form of packets by a packet-switched network. Exemplary circuit emulation services are the PWE3 (PseudoWire Emulation Edge-to-Edge), the “TDM over MPLS” and the CESoETH (Circuit Emulation Service over Ethernet).
The implementation of a circuit emulation service for connecting two users typically requires to connect each of the two users to the packet-switched network by means of a respective interface which provides an interworking function between the TDM traffic flows and the packet-switching service supported by the packet-switched network.
In particular, in the direction entering the packet-switched network, each interface receives a TDM traffic flow from its respective user, it converts such a TDM traffic flow into a packet sequence and it transmits the packet sequence towards the other interface through the packet-switched network. Further, in the direction exiting the packet-switched network, each interface receives a further packet sequence from the other interface through the packet-switched network, it processes the further packet sequence thus recovering a further TDM traffic flow, and it transmits the further TDM traffic flow to its respective user.
Converting the TDM traffic flow in a packet sequence typically requires splitting the TDM traffic flow into portions of a predefined size and inserting each portion into the payload of a respective packet. Then, for each packet, a respective header is generated.
For instance, the standard MEF8 by the Metro Ethernet Forum, October 2004, defines the above mentioned CESoETH service. In particular, the standard MEF8, par. 6, describes to split the TDM traffic flow into portions, to insert each portion into the payload of an Ethernet packet, and to generate for each Ethernet packet a 38 byte-long header, in turn comprising: an Ethernet service layer header of 14 bytes, an adaptation header of 8 bytes, an RTP (“Real-time Transfer Protocol”) header of 12 bytes and a frame check sequence of 4 bytes.
Similarly, the recommendation Y.1413 by ITU-T, March 2004, defines the above mentioned “TDM over MPLS” service. In particular, the recommendation T.1413, par. 8 and 9, discloses to split the TDM traffic flow into portions, to insert each portion into the payload of an MPLS packet, and to generate for each MPLS packet a 24 byte-long header, in turn comprising: a transport label of 4 bytes, an interworking label of 4 bytes, interworking common indicators with an overall size of 4 bytes and an RTP header of 12 bytes. A 14 byte-long Ethernet service layer header and a frame check sequence of 4 bytes have then to be added.
EP1176774 discloses a method for processing one or more TDMs for communication over IP networks, such as the Internet, including encapsulating ATM cells (packets) using AAL1 cells within UDP over IP frames to provide synchronous bit streams into fixed size cells. This allows for an IP header to be added to the packets, with such packets forwarded to its destination host across the IP network. The destination regenerates the clock, decrypts/strips the IP header and delivers a synchronous bit stream. Furthermore, an adaptive clock is provided for clock transfer across the network. The adaptive clock regenerates the far end T1/E1 receive clock out of the incoming arrival frame rate. Frames arriving from the IP network are stored in a buffer and taken out for TDM stream assembly.
US 2003/172257 discloses systems and methods for implementing: a rings architecture for communications and data handling systems; an enumeration process for automatically configuring the ring topology; automatic routing of messages through bridges; extending a ring topology to external devices; write-ahead functionality to promote efficiency; wait-till-reset operation resumption; in-vivo scan through rings topology; staggered clocking arrangement; and stray message detection and eradication.